The present invention relates to the configuration of a fluorescent lamp. In particular, the present invention relates to the configuration of a fluorescent lamp that can achieve a smaller lamp shape for the same lamp characteristics.
FIG. 10 shows a light-emitting tube 27 used in a conventional compact fluorescent lamp. The light-emitting tube 27 includes two straight glass tubes 32, 33. One end of each of glass tubes 32, 33 is closed, and the other end is sealed with stems 31 for supporting electrodes 29, 30, respectively. The glass tubes 32, 33 are connected at the one end portion by a bridge junction 34. A discharge space is formed in the light-emitting tube 27 through the bridge junction 34. A phosphor 28 is applied to the inside surface of each of the glass tubes 32, 33. The light-emitting tube 27 is filled with mercury and a buffer inert gas. A resin base 35 is attached to the end of the light-emitting tube 27 on the stem side, thus providing a so-called single-base compact fluorescent lamp as a finished product.
The conventional compact fluorescent lamp as mentioned above has a small lamp shape and is characterized by high efficiency and long life.
For example, a 36W type compact fluorescent lamp as shown in FIG. 10, which is a major product for a supply voltage of 200V, has a lamp length of 410 mm. This is about one third of the lamp length (1198 mm) of a 40W type straight fluorescent lamp whose luminous flux is substantially the same as that of the 36W type compact fluorescent lamp. The 36W type compact fluorescent lamp can have the lamp characteristics such as a luminous flux of 2900 lm, a lamp efficiency of 80.5 lm/W, and a lamp life of 9000 hrs. The tube outer diameter of the compact fluorescent lamp is reduced to 20 mm compared with 32 mm for the 40W type straight fluorescent lamp. The discharge path length (i.e., a distance between the electrodes) of the compact fluorescent lamp also is reduced to about 730 mm compared with about 1100 mm for the 40W type straight fluorescent lamp. Both the compact fluorescent lamp and the straight fluorescent lamp have a lamp current of 430 mA.
A 96W type compact fluorescent lamp has a lamp length of 860 mm, which is about one third of the lamp length (2367 mm) of a 110W type straight fluorescent lamp whose luminous flux is substantially the same as that of the 96W type compact fluorescent lamp. The 96W type compact fluorescent lamp can have the lamp characteristics such as a luminous flux of 8600 lm, a lamp efficiency of 89.6 lm/W, and a lamp life of 7500 hrs. The tube outer diameter is 22 mm, and the lamp current is 820 mA.
While the compact fluorescent lamps as mentioned above are made smaller than the conventional straight fluorescent lamps, they are still larger than the incandescent lamps that are almost point light source or high-pressure discharge lamps. A further reduction in size of a compact fluorescent lamp makes it possible to design a smaller lighting fixture that can facilitate light distribution control with high efficiency, which may further improve energy saving and lighting design quality. However, there is a limit to such a reduction in lamp shape of the conventional compact fluorescent lamps because they use a bending or junction process to form a continuous discharge path inside the glass tubes as described above.
Before developing the conventional compact fluorescent lamps, various kinds of light-emitting tube configurations were proposed.
For example, FIG. 11 schematically shows the configuration of a light-emitting tube used in a so-called internally partitioned lamp (R. G. Young et al., xe2x80x9cA compact partition fluorescent lamp,xe2x80x9d Lighting Design and Application, May 1980, pp. 38-42). Alight-emitting tube 36 includes a straight glass tube 37 wherein the inside surface is coated with a phosphor. The internal space of the straight glass tube 37 is divided by insulating walls 38 into a plurality of portions so as to provide a continuous discharge path. A pair of electrodes 39, 40 are located at the ends of the discharge path, respectively. This configuration can achieve a smaller lamp shape.
FIG. 12 schematically shows the configuration of a light-emitting tube used in a so-called multi-arc lamp (Mikiya YAMANE et al., xe2x80x9cShunt mechanism for a discharge tube having two discharge paths,xe2x80x9d Journal of the Illuminating Engineering Society, vol. 63, No. 9 (1979), pp. 19-25). In a light-emitting tube 41, a glass stem 43 is provided at one end of a glass bulb 41 so as to seal and support the end of a glass inner tube 44. An electrode 45 that functions as a cathode is attached inside the glass inner tube 44 by the glass stem 43. Two electrodes 46, 47 that function as an anode are attached near the one end of the glass bulb 42. This lump is turned on by the application of a direct current, and two discharge arcs are generated between the cathode 45 and each of the anodes 46, 47.
FIGS. 13A and 13B schematically show two configurations of light-emitting tubes used in a multiple-tube fluorescent lamp disclosed by JP 8(1996)-315772 A. Alight-emitting tube 48 in FIG. 13A has a double-tube structure in which the necessary portion of an envelope 49 is coated with a phosphor, two external electrodes 50 are provided at the bottom, a transparent inner tube 51 that transmits ultraviolet rays is placed in the envelope 49, and an internal electrode 52 is provided at the bottom of the transparent inner tube 51. Alight-emitting tube 53 in FIG. 13B has a triple-tube structure in which the necessary portion of an envelope 54 is coated with a phosphor, an external electrode 55 is provided at the bottom, double transparent inner tubes 56, 57 that transmit ultraviolet rays are placed in the envelope 54, and an internal electrode 58 is provided at the bottom of the transparent inner tube 56.
The studies conducted by the present inventors on various compact fluorescent lamps proposed so far with the above configurations show that it is very difficult to make those compact fluorescent lamps commercially available as products. For example, the lamp configuration in FIG. 11 cannot reliably prevent a so-called discharge crosstalk between adjacent discharge paths that are partitioned by the insulating wall 38. The lamp configuration in FIG. 12 cannot easily achieve high efficiency in the lamp characteristics, and also has a limit of providing a smaller lamp shape. The lamp configuration in FIG. 13A cannot easily achieve high efficiency in the lamp characteristics. For this configuration, it is more difficult to place the ultraviolet-ray transmitting inner tube 51 in the envelope 49, the inner tube 51 using a different glass material from that of the envelope 49. Similarly, for the lamp configuration in FIG. 13B, it is much more difficult to place the double inner tubes 56, 57 in the envelope 54, the double inner tubes 56, 57 using a different glass material from that of the envelope 54.
Therefore, to improve energy saving and lighting design quality by promoting the spread of compact fluorescent lamps, it is a major challenge to find a novel lamp configuration that can achieve a much smaller lamp shape than the conventional technique.
It is an object of the present invention to provide a compact fluorescent lamp that can achieve a much smaller lamp shape without degrading the lamp characteristics and contribute to further improvements in energy saving lighting and lighting design quality.
A fluorescent lamp of the present invention includes two glass outer tubes, a bridge junction, and first glass inner tubes. One end of each of the glass outer tubes is closed, and the other end is sealed with stems for supporting electrodes, respectively. A phosphor is applied to the inside surface of each of the glass outer tubes. The bridge junction connects the glass outer tubes at the other end portion to form a discharge space inside the glass outer tubes. The first glass inner tubes are provided in the glass outer tubes, respectively. A phosphor is applied to the surface of each of the first glass inner tubes. One end of each of the first glass inner tubes is open and disposed at the closed ends of the glass outer tubes, and the other end is sealed with the tips of the stems so that the electrodes are positioned in the first glass inner tubes.
This configuration allows a fluorescent lamp to have a much shorter and smaller lamp shape as well as better lamp characteristics than a conventional compact fluorescent lamp.
Another fluorescent lamp of the present invention includes two glass outer tubes, a bridge junction, first glass inner tubes, and second glass inner tubes. One end of each of the glass outer tubes is closed, and the other end is sealed with stems for supporting electrodes, respectively. A phosphor is applied to the inside surface of each of the glass outer tubes. The bridge junction connects the glass outer tubes at the one end portion to form a discharge space inside the glass outer tubes. The first glass inner tubes are provided in the glass outer tubes, respectively. A phosphor is applied to the surface of each of the first glass inner tubes. The second glass inner tubes are provided in the glass outer tubes so that the first glass inner tubes are inserted into the second glass inner tubes, respectively. A phosphor is applied to the surface of each of the second glass inner tubes. One end of each of the first glass inner tubes is open and disposed at the closed ends of the glass outer tubes, and the other end is sealed with the tips of the stems so that the electrodes are positioned in the first glass inner tubes. The ends of the second glass inner tubes are open at least on the stem side.
This configuration further can reduce the length and size of a lamp shape as compared with the above configuration.
In this configuration, it is preferable that protrusions are formed at the insides of the closed ends of the glass outer tubes, and the other ends of the second glass inner tubes are sealed with the protrusions.
In the above configurations, it is preferable that the glass inner tubes are disposed eccentrically from the central axes of the glass outer tubes toward the bridge junction. This deviation forms a small discharge space on the bridge junction side and a large space on the opposite side, so that a discharge is caused to occur easily in the large space. Therefore, the brightness of light emitted from the outside surface of a light-emitting tube, i.e., the portion of the glass outer tubes other than the surfaces that are opposed to each other via the bridge junction can be increased as compared with a configuration in which the glass inner tubes and the glass outer tubes are arranged coaxially. Further, a discharge loss is suppressed.